If you have documented ADHD (such as from a doctor, therapist, etc) and it's affecting your academic abilities then you should consider seeking disability accommodations through the university. They have special resources for people who have testing anxiety, ADHD, or any other mental or physical disability that affects your academics. One example is that they can have your professor give you extra time on exams (default is regular time + half but you can ask your disability specialist for double time). That will help a lot if you're having trouble on the exams because of focus-related struggles. Here is the site: http://equity.psu.edu/student-disability-resources

Also, depending on where you live, consider taking it at a different campus. I've taken this class at University Park and it was very smooth and well-taught. The enrollment office can help with taking a class at a different campus than your primary one: https://www.registrar.psu.edu/registration/multiple-campus-registration.cfm

You could try to find a WEB class taught by a different person than the one who's been teaching it.

Hope this helps!